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Relationships between Cholecalciferol Metabolism and Growth in Chicks as Modified by Age, Breed and Diet¹

Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

Fast-growing heavy (White Rock) chicks, fed a vitamin D-deficient diet, exhibited a higher activity of kidney 25-hydroxycholecalciferol-1-hydroxylase (1-hydroxylase) than slow-growing light (White Leghorn x Rhode Island Red) chicks fed the same diet. 1-Hydroxylase and duodenal calcium-binding protein (CaBP) declined with age. Feeding of low energy diets with or without vitamin D resulted in a slower rate of growth and reduced 1-hydroxylase activity and CaBP concentration. Severe dietary restriction of either calcium or phosphorus resulted in a lower growth rate as well as a duodenal CaBP as compared to a moderate mineral restriction. The severe dietary calcium restriction also resulted in a lower 1-hydroxylase activity than that resulting from a moderate restriction. The results clearly indicate that high 1-hydroxylase activity and a high intestinal CaBP are associated with a high growth rate.

KEY WORDS: • Vitamin D deficiency • calcium-binding protein

¹ Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 208-E, 1980 series. The research was supported by the Poultry Marketing Board of Israel.

Manuscript received 9 July 1980.